The ESL is generally an inductance component existing in a path from the connection point of a capacitor to the ground point in a main line. In an equivalent circuit including the ESL, the capacitor does not function at a frequency higher than a self-resonance frequency determined by capacitance of the capacitor and the ESL. That is, the ESL is a factor that degrades filter performance of the capacitor.
Patent Literature 1 describes a circuit module having a structure for canceling such ESL (hereinafter referred to as an ESL cancellation structure).
In the ESL cancellation structure described in Patent Literature 1, a first power supply line and a second power supply line are connected together at one connection point, and the connection point and the ground are connected together by a grounding line. A bypass capacitor is connected in series in the middle of the grounding line.
The first power supply line is connected in series to a first inductor, and the second power supply line is connected in series to a second inductor. In addition, the first inductor and the second inductor are arranged to generate mutual induction such that the inductance thereof and the inductance of a parasitic inductor in the grounding line are the same in the magnitude and inverse to each other in their signs. Note that, inductance of a combined inductor of the parasitic inductor in the grounding line and a parasitic inductor in the bypass capacitor corresponds to the ESL.
In the above ESL cancellation structure, a mutual inductor generated by the mutual induction between the first inductor and the second inductor is adjusted to be equal to the ESL.
With this configuration, a result equivalent to the case where no inductance component exists in a path from the connection point between the first power supply line and the second power supply line to the ground point is obtained.
Therefore, in a filter using a bypass capacitor, it is possible to reduce degradation of the filter performance due to influence of the ESL.